A semiconductor integrated circuit formed in a semiconductor chip is coupled to an external circuit via an external terminal (pad) of the semiconductor chip. Japanese Laid-Open Patent Publication Nos. 2004-282660 and 2006-311201 describe a semiconductor integrated circuit including an input and output circuit that inputs and outputs a signal from and to an external circuit.
For example, the semiconductor integrated circuit outputs a digital signal from an output circuit to a certain terminal. Further, the semiconductor integrated circuit sets the output circuit into a high-impedance state and receives a digital signal from that terminal.
In a sequential comparison type A/D converter, every time A/D conversion of each bit is performed, a capacitor is charged and discharged by an output signal from a D/A converter so as to change a comparison voltage. In other words, an output signal from the D/A converter to be used for charging and discharging the capacitor changes according to a comparison result of a previous bit. A time required for charging and discharging the capacitor is influenced by an increase in speed of the A/D conversion. However, when the increase in speed of the A/D conversion shortens a charge/discharge cycle period, the capacitor may not be sufficiently charged and discharged. As a result, a voltage difference is caused between a voltage according to a comparison result of previous bit and a comparison voltage obtained by the charging and discharging of the capacitor. This voltage difference causes erroneous determination in an operation for comparing a next bit. This deteriorates accuracy of a digital output signal.